1. Field of the Invention
The present invention relates to an EGR valve having a valve stem bearing and coupling configuration which eliminates friction and binding caused by side-to-side loading in the bearing area.
2. Description of the Relevant Art
Typical Exhaust Gas Recirculation (EGR) valves are used to control exhaust gas recirculation in an internal combustion engine. The EGR valve generally comprises a valve, positioned by an actuator to meter the exhaust gas which passes through the valve. The actuator retracts the valve from a seat to increase recirculation of exhaust gas, and advances the valve toward the seat to reduce recirculation of gas. The seat is incorporated in a base that mounts the valve on the engine manifold.
Alignment of the valve and the valve seat is critical. Misalignment between the two components will create a path for gas leakage to the engine when not desired, cause exhaust gas flow variability, and result in wear of the valve and seat. To achieve accurate alignment, it is desirable to maintain the valve stem in precise, coaxial alignment with the valve seat through the use of a precision valve stem bearing. However, such precise mounting is difficult to achieve because of the tendency for friction between the bearing and stem, caused by side-to-side loading of the stem by the actuator, to cause binding of the shaft in the bearing. This side-to-side loading is generally a result of misalignment between the valve stem and the actuator which is rigidly attached to the stem and not aligned coaxially with the valve seat. Actuator alignment is very difficult to maintain due to the many components involved.